BIOL 273 - Unit 3.3 Flashcards
What happens to A band during muscle contraction
remains constant - therefore myosin shortening could not be responsible for muscle contraction
Describe the sliding filament theory
- At rest the ends of thick (myosin) and thin (actin) filaments overlap slightly within each sarcomere
- Thick and thin filaments slide past each other with no change in the length of the filaments themselves
- The thin (actin) filaments slide along the thick (myosin) filaments towards the M line of the sarcomere - brings the Z disks closer together
What happens to the H zone during the sliding filament theory
decreases
What happens to the A band during sliding filament theory
remains constant
What happens to the Z discs during the sliding filament theory
closer to M line
What happens to the I band during the sliding filament theory
decrease
What do skeletal muscles need to be stimulated by to contract
somatic motor neuron from the nervous system
What is released by the neuron into the synaptic cleft at the neuromuscular junction, what does this neurotransmitter bind to?
- ACh released
- binds to nicotinic cholinergic receptors on highly folded muscle motor end plates (aka Na+/K+ channels)
What happens when ACh binds to Na+/K+ channels
- allows Na+ and K+ to move across the membrane
- ACh is removed by acetylcholinesterase
- Na+ influx exceeds K+ efflux
What happens when Na+ influx exeeds K+ efflux , what is it called
local depolarization occurs at the synapse
- called End Plate Potential - EPP
What happens during depolarization , EPP, what structure does it interact with
the potential moves down the T-tubule system
- T tubule membrane contains dihydropyridine (DHP receptors) - L type calcium channel
What happens on the T-tubule membrane when it is depolarized
- DHP receptors changes conformation
- they are mechanically linked to Ca 2+ channels of the SR called ryanodine receptors (RyR)
- RyR changes conformation whih allows for opening of SR Ca+2 channels (calcium leaves the SR)
- increasing cytosolic Ca2+
What happens when calcium is roaming free in the cytosol
Ca+2 binds to troponin on the thin filament
- this moves tropomyosin into the “on” position revealing actin binding sites
the binding of calcium and acting on regulatory proteins on thin filament results in what process
the crossbridge cycle
What is myosin’s function in the crossbridge theory
converting chemical energy (ATP) into movement
What are the binding sites of myosin
actin and ATP
When does myosin bind to actin during the crossbridge cycle
when actin is exposed when Ca2+ binds to troponin
- this forms the crossbridge
What happens when the myosin heads binds to actin during crossbridge cycle , what is this process called
inorganic phosphate releases from myosin (1st)
- causes myosin head to pivot toward the centre of the sarcomere
- called the powerstroke
- pulls thin filament towards the M line
- followed by the released of ADP from myosin (2nd)
When does the myosin head (crossbridge) detach
when a new molecule of ATP attaches to the myosin head
When does the myosin head return to the cocked position
when the myosin head ATPase hydrolyses ATP to ADP and Pi
When does relaxation of the skeletal muscle occur
When Ca2+ is pumped back into SR through the Ca2+ ATPase (against concentration gradient)
- decrease in calcium in cytosol causes troponin and calcium to unbind
- troponin shift to too position and covers binding site on actin of thin filament
When does Glycolysis occur , what does it produce
in the presence or absence of oxygen
- provides limited amount of ATP - 2
- produces lactic acid
Creatine phosphate
high energy phosphate molecule
- highly concentrated in muscles , provides a rapid source of energy
- easily donates inorganic phosphate to ADP to create ATP (provides a limited supply of ATP)
Purpose of creatine phosphate
buffer concenration of ATP over very short time
creatine + ADP to ATP + creatine
(catalyzed by creatine kinase)
